Alpha-hydroxyisobutyric acid has been prepared by oxidizing an aqueous solution of the corresponding alcohol in the presence of a base and a platinum catalyst as shown for example in C. K. Heyns and H. Paulsen, "Newer Methods of Preparative Organic Chemistry" Vol. II, pp. 303 (1963).
As described in an article by E. F. Schoenbrunn and J. H. Gardner, J. Am. Chem. Soc., Vol. 82, pp. 4905 (1960) and U.S. Pat. Nos. 2,847,453, 2,847,454 and 2,847,465 .alpha.-hydroxyisobutyric acid may be produced by the liquid phase oxidation of isobutylene with nitrogen tetroxide and nitric acid.
An article by E. C. Taylor, H. W. Artland and G. McGillivray, Tetrahedron Letters, No. 60, pp. 5285-5288 (1970) discloses the preparation of for example, .alpha.-isobutoxyiso-butyric acid using thallium (III) acetate with an excess of neat isobutyric acid to prepare a thallium (III) carboxylate and acetic acid with removal of the acetic acid by distillation and reflux under nitrogen of the thallium (III) carboxylate in an isobutyric acid solvent to give the .alpha.-acyloxycarboxylic acid.
U.S. Pat. No. 3,897,489 discloses a method for the production of alpha-hydroxyisobutyric acid by the catalytic oxidation of isobutylene glycol with molecular oxygen in the presence of a supported platinum catalyst.
The process of the present invention provides a high yield selectivity to the .alpha.-hydroxyisobutyric acid by the stoichiometric oxidation of isobutyric acid with thallic salts. Isobutyric acid is readily available from oxidation of isobutyraldehyde obtained for example as a by-product in n-butyraldehyde/n-butanol production.
The .alpha.-hydroxyisobutyric acid product of this invention may be dehydrated to methacrylic acid by known methods, as shown for example in U.S. Pat. No. 3,562,320 (1971), or reacted with methanol to give methyl methacrylate directly as described in British Pat. No. 852,664.